In recent years, CDMA 2000 1X-EV DO (hereinafter, referred to as ‘EV-DO’) system has been developed as a high-speed wireless communication system of next generation. The CDMA 2000 1X system, in which the CDMA One system is extended so as to correspond to a third-generation system, has been further specialized for data communication to speed up a transmission rate, thereby constructing the EV-DO system. Here, the term ‘EV’ stands for ‘evolution’ and the term ‘DO’ stands for ‘data only’. Generally, a mobile communication system has been built up for a voice call by using a mobile phone, a car-phone, and a personal handy phone system. At present, a data communication system is used for general data communication including a portable computer such as a PDA (Personal Digital Assistance). A wireless communication network which has been connected to a conventional wired telephone network, and of which service area has been rapidly enlarged has become a social infrastructure.
Further, a communication band of a wireless communication network such as a wireless LAN (Local Area Network) has been enlarged.
(Patent Document 1) JP-A-2002-300644
When a mobile communication terminal belongs to any communication network, the mobile communication terminal is generally assigned with an IP (Internet Protocol) address from an access point or a base station which manages the communication network. The assigned IP address is valid as long as the mobile communication terminal belongs to the communication network. When the mobile communication terminal belongs to another communication network, the mobile communication terminal is assigned with an IP address valid in the newly belonging communication network.
Accordingly, in order to perform data transmission from a communication apparatus to a mobile communication terminal, it is necessary to specify a communication network to which the mobile communication terminal as a communication target currently belongs. This is because an IP address for specifying the mobile communication terminal is determined by the communication network to which the mobile communication terminal belongs.
A communication protocol called as a mobile IP has been designed and put to practical use so as to cope with the problems peculiar to the mobile communication. According to the mobile IP, the communication apparatus can perform communication regardless of the communication network to which the mobile communication terminal to be a destination of data transmission currently belongs.
However, the mobile IP is a communication protocol which has been designed based on a single communication interface. Hence, a mobile communication terminal which has a plurality of communication interfaces for accessing various communication networks such as mobile phones or wireless LANs will be generalized. For example, a mobile communication terminal normally performs communication via a wireless LAN which is a communication network to which the mobile communication terminal belongs. Alternatively, when the mobile communication terminal does not belong to the area of the wireless LAN, the mobile communication terminal may perform communication via a mobile phone network. The mobile IP does not include logic for causing the mobile communication terminal having the plurality of communication interfaces to provide its functions.
The invention has been made in consideration of the above-described problems, and it is an object of the invention to provide a technology which allows a mobile communication terminal to select one of a plurality of communication interfaces and to perform mobile communication.